Photochromic glasses function as sun glasses by prompt color development outdoors where a light containing ultraviolet light such as sunlight is applied to the glasses and function as ordinary transparent glasses by color fading indoors where no such light is applied to the glasses. The demand for the photochromic glasses is growing in recent years.
As a method for manufacturing plastic lenses having photochromic properties, there have been known a method in which a photochromic compound is allowed to impregnate the surface of a lens having no photochromic properties (impregnation method); a method in which a photochromic compound is dissolved into a monomer, and the monomer is polymerized to directly give a photochromic lens (kneading or in-mass method); and a method in which a layer having photochromic properties (hereinafter sometimes referred to as the photochromic coat layer) is formed on the surface of a plastic lens by using a coating liquid containing a photochromic compound (hereinafter sometimes referred to as the photochromic coating agent) (coating method). Among them, the coating method has a merit that, in principle, the photochromic properties can be imparted easily to any lens substrates as compared with the other two methods. For instance, in the impregnation method, it is necessary to use a soft lens substrate as the substrate lens so that a photochromic compound may easily diffuse into it. Further in the kneading or in-mass method, a special monomer composition needs to be used in order to realize good photochromic properties. In contrast, in the coating method, there are no such restrictions in the substrates.
When a photochromic plastic lens is manufactured by the coating method, the thickness of a photochromic coat layer formed on the surface of a lens substrate is thin. Therefore, in order to obtain a photochromic coat layer having practical color optical density, the coat layer needs to contain a photochromic compound in a high concentration. As such photochromic compounds, chromene derivatives are widely used, and especially from the viewpoints of excellent color development and rapid fade rate, alkylamino group-containing or dialkylamino group-containing chromene derivatives are sometimes used (refer to Patent Documents 1 and 2).
In addition, on the photochromic coat layer, a hard coat layer is formed in order to improve scratch resistance of the optical substrate. For instance, in the Patent Document 1, an example using a hard coat agent 1 (trade name TS56H, manufactured by Tokuyama Corp.) is described. In the Patent Document 1, when a hard coat layer is formed on a photochromic coat layer, a hard coat liquid not containing a tetraalkoxy silane nor a methyl trialkoxy silane is used because of the pot-life problem of the hard coat agent (a storage period for which the hard coat agent keeps physical properties to realize expected effects after preparation of the hard coat agent is short).    Patent Document 1: WO 2003/011967    Patent Document 2: Japanese Patent Application Laid-Open